Many monitoring, measuring and input devices utilize scan mirrors to optically scan a field of view. For example, weather satellites, such as the GOES satellite, incorporate scan mirrors for scanning weather patterns over earth. In the GOES satellite, the scan mirror reflects to a detector light received from a portion of the atmosphere at which the mirror is directed. The precise pointing direction of the scan mirror is important, as the detected radiation represents atmospheric data, such as cloud and precipitation data, collected from a precise portion of the earth's atmosphere. This pointing direction is then used to correlate the atmospheric data collected with the underlying geography of the earth for depiction of weather conditions on weather maps. Other instruments which may have scan mirrors include semiconductor wafer scanners and photocopying machines. In each of these applications, it is necessary to accurately track and control the position of the scan mirror.
In the case of satellite and semiconductor wafer scanning mirrors, the scan mirror may operate in a vacuum and under extremes of temperature. In the case of a scan mirror located in a photocopying machine, the scan mirror may be subject to large temperature fluctuations when the photocopier goes from a resting state to a state of continuous copying.
The characteristics of the scan mirror may change over temperature and pressure extremes. Therefore, it is desirable to have a device to measure the accuracy of and calibrate a scan mirror over a wide range of temperatures and pressures. It would further be desirable to have a device for measuring scan mirror angles with high accuracy, which itself requires setup and manual manipulation only one time.
Prior art devices, such as theodolites, exist for measuring angles. However, theodolites are limited in their angle measuring accuracy.